(1) Field of the Invention
The present invention generally relates to an apparatus and method for detecting acoustic signals from a plurality of acoustic signal sensors.
(2) Description of the Prior Art
Prior art acoustic signal detection devices typically use complex signal processing circuitry which conditions acoustic signals and performs signal processing functions upon such signals, e.g., Fast Fourier Transforms, to extract desired data. Such a device is disclosed in U.S. Pat. No. 4,017,859. Other prior art devices measure the cross-spectral density of received acoustic signals to determine the acoustic density in a particular direction. Such a device is disclosed in U.S. Pat. No. 4,982,375. Additionally, many prior art devices use complex circuitry to perform phase and magnitude detection and to effect conversion from rectangular to polar coordinates. One such device is described in U.S. Pat. No. 4,953,145. Still, other prior art devices utilize circuitry for the generation of frequency tones. For example, U.S. Pat. No. 3,588,802 utilizes a mechanical vibrator for exciting a frequency tone that is added to the received acoustic signal. Other prior art devices use a pair of hydrophones wherein each hydrophone is dedicated to receiving particular frequency components of acoustic signals. For example, U.S. Pat. No. 4,594,695 discloses a system that utilizes two hydrophones wherein one hydrophone receives a disturbed tracked signal and the other hydrophone receives spurious noises.
What is needed is a relatively less complex acoustic signal detection system that provides redundancy whereby the acoustic signal detection system receives and detects acoustic signals from a plurality of acoustic signal sensors (e.g. hydrophones) as long as one of the acoustic signal sensors senses an acoustic signal. Preferably, the redundancy should be realized by the overall design of the acoustic signal detection system so as to substantially increase the probability that acoustic signals sensed by the sensors will still be detected by the acoustic signal detection system even if this system experiences partial component failure. Another desired feature of such an acoustic signal detection system is that it must be relatively simple in construction in order to reduce the costs related to manufacturing, maintenance and repair.
Therefore, it is an object of the present invention to provide an apparatus and method for receiving and detecting acoustic signals from a plurality of acoustic signal sensors that fulfills a long-felt need that has not been met by prior art devices and methods.
Other objects and advantages of the present invention will be apparent to one of ordinary skill in the art in light of the ensuing description of the present invention.
The present invention is directed to an apparatus and method for detecting acoustic signals from a plurality of acoustic signal sensors. The apparatus comprises a plurality of acoustic signal detection channels. Each acoustic signal detection channel has an input for receiving acoustic signals from a corresponding acoustic signal sensor. Each acoustic signal detection channel further includes circuitry for (i) amplifying the received acoustic signals, (ii) removing the D.C. components from the amplified acoustic signals, and (iii) removing all frequency components from the amplified acoustic signals which are above a predetermined frequency. The apparatus further comprises circuitry for summing all of the acoustic signals outputted from the acoustic signal detection channels to form a single acoustic signal. The apparatus further comprises additional circuitry for converting the single acoustic signal into a differential signal and outputting the differential signal if at least one acoustic signal sensor senses an acoustic signal and the corresponding acoustic signal detection channel outputs an acoustic signal.